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What Is Carbon Fiber-Ultimate Guide

Views:50 Author:Iris Publish Time: 2024-05-24 Origin:

 What Is Carbon Fiber and Carbon Fiber Products-Ultimate Guide

1.History of Carbon Fiber

Carbon fiber was first made by Joseph Wilson Swan in 1860 for early incandescent light bulbs. In the 1950s, to solve the problem of high temperature and corrosion resistance in strategic materials, there was a global push to develop and manufacture carbon fiber again. In 1959, Japan invented PAN-based carbon fiber with a carbon content of 95%. This improved its tensile strength and elasticity, leading to its use in high-end fields like aerospace. Since the 21st century, as carbon fiber technology has matured, production capacity has expanded, and costs have dropped. This has allowed carbon fiber to be used in civilian areas such as wind power, pressure vessels, medical equipment, and sports goods.


2.What Is Carbon Fiber?

Carbon fiber is a high-strength, high-modulus fiber with over 95% carbon content and a diameter of 5-8 microns. It is made through a process of high-temperature carbonization. Although it has better mechanical and corrosion resistance properties than steel, its high production cost limits its use in civilian fields to mainly high-end products. It is typically used as a reinforcement material in resin-based composites, suitable for applications requiring high strength, high modulus, low weight, fatigue resistance, corrosion resistance, and X-ray transparency.


3.Types Of Carbon Fibers

There are many types of carbon fiber, each with different properties and forms, leading to significant price differences. Different applications have different requirements for carbon fiber. Understanding the classification of carbon fiber can help you choose the right material to meet your specific needs. The main classification methods are as follows:

3.1 Based on Precursor Fiber Materials:

Carbon fiber can be classified based on precursor materials and production processes into PAN-based carbon fiber, rayon-based carbon fiber, pitch-based carbon fiber, and vapor-grown carbon fiber. Among these, PAN-based carbon fiber is the most widely used, accounting for over 90% of global production. The production process for PAN-based carbon fiber includes spinning, oxidative pretreatment, carbonization, graphitization, and surface treatment. This method offers high carbonization rate and superior performance.

3.2 Based on Numbers of Filaments

Carbon fibers can also be classified based on the number of filaments in a bundle:

Small Tow - Carbon fiber with a filament count of ≤24K (1K = 1000 individual filaments). It is mainly categorized into 1K, 3K, 6K, 12K, and 24K. Small tow carbon fibers find applications in military (aircraft, missiles, satellites) and sports and entertainment goods (fishing gear, golf heads, badminton rackets). They are characterized by high production costs, low output, and high prices. The widely used carbon fiber products in the market are typically composed of 3K (surface appearance) + 12K (UD structural components). The T300 and T700 grades are the most commonly used.

Large Tow - Carbon fiber with a filament count of ≥48K (1K = 1000 individual filaments). It is mainly available in 48K, 60K, and 80K variants. Large tow carbon fibers are primarily used in industrial sectors such as textiles, pharmaceuticals, transportation, civil engineering, and energy. Currently, wind turbine blades are the most widely used.

3.3 Types by Mechanical Properties

UHM-Ultra High Elastic Modulus

  • Tensile Elastic Modulus≥600 GPa

  • Tensile Strength: ≥2,500 MPa

HM-High Elastic Modulus

  • Tensile Elastic Modulus: 350-600 GPa

  • Tensile Strength: ≥2,500 MPa

IM-Intermediate Elastic Modulus

  • Tensile Elastic Modulus: 280-350 GPa

  • Tensile Strength: ≥3,500 MPa

HT-Standard Elastic Modulus

  • Tensile Elastic Modulus: 200-280 GPa

  • Tensile Strength: ≥2,500 MPa

LM-Low Elastic Modulus

  • Tensile Elastic Modulus: ≤200 GPa

  • Tensile Strength: ≤3,500 MPa


4.What Does Carbon Fiber Look Like?

Carbon Fiber Weaves and Patterns:

  • The most common appearance of carbon fiber is the 3K twill/plain weave. The 3K pattern is a typical carbon fiber texture, where each filament reflects a three-dimensional texture under light, giving it a high-tech feel and making it popular.

  • Additionally, the 1K and 12K plain weaves, as well as the UD (unidirectional)      appearance, are also quite common.

  • 1K is often used for smaller precision parts, such as watch frames and straps. It's the most expensive, and plain weave is more commonly used.

  • On the other hand, 12K is widely used in sports equipment like pickleball paddles, hockey sticks, and larger surface components. Grid patterns of 8mm/18mm/22mm width are common.

  • The UD appearance is more affordable and is typically used for products with low-cost and low-weight requirements, such as telescopic poles and masts.

  • The Satin weaved pattern is created by machines weaving carbon fiber yarn into a specific pattern. Unlike the 3K twill or plain weave patterns, satin weave has a stronger three-dimensional effect and a more exquisite appearance. It incurs higher production costs and is mainly used in car interiors and exterior parts for sports cars.


5.How To Make Carbon Fiber Parts?

The shape and strength requirements of carbon fiber products determine the layering method, carbon fiber production process, and equipment used. Technicians need to ensure product quality while choosing the most cost-effective carbon fiber fabrication process.

5.1 Carbon Fiber Tubes: 

Carbon fiber tubes can typically be classified based on production processes and shape requirements into pultrusion, roll-wrapping, filament winding, and molding processes.

  • Pultrusion: This process produces straight tubes, including rectangular and hexagonal shapes. Carbon fiber tows are immersed in resin and extruded into molds under traction conditions for curing. It offers low-cost continuous production of fixed-section products but may have challenges in controlling accuracy and shear strength.

  • Roll-wrapping: Used for round straight tubes, it involves wrapping pre-cut prepreg materials onto a mandrel with a rolling machine, followed by curing and demolding under controlled conditions. Structural design and carbon fiber layup orientation can enhance strength in different directions, with post-processing for improved straightness and roundness.

  • Filament winding: Carbon fiber yarn is wound onto a mandrel in designed directions under tension and cured under heat to produce products, mainly used in the production of pressure vessels and electric insulation products.

  • Molding processes: Using carbon fiber prepreg material as raw material, it can meet strength requirements in different directions through layering and structural design. It can produce curved pipes of different thicknesses and embed metal fittings. Unlike the three production methods mentioned above, high-pressure molding results in pipes with higher strength and precision. Mass production increases mold efficiency and capacity. However, since laying is done manually without automation, the product's price is relatively high

5.2 Carbon Fiber Sheets:

The production process of carbon fiber sheets involves cutting prepreg materials, layup, and curing and molding using either a molding press or an autoclave machine.

  • Molding Press Production: The equipment used in molding press production limits the size and thickness of carbon fiber sheets. Sheets produced by molding presses typically do not exceed 1500x2500mm, suitable for small-sized sheets. Molding presses longer than 3 meters are rare in the market, so an autoclave machine is recommended if the size is larger than 2500mm.

  • Autoclave Machine Production: The dimensions of the autoclave machine  chamber limit the maximum size of the sheets. Our largest sheet size achievable is 3000x9000mm.

  • For sheets of the same size, those produced by molding presses have higher strength due to the greater pressure applied during production. However, resin flow to the edges under pressure can lead to surface defects like pores and pinholes. Therefore, for thicknesses such as 0.2mm and 0.5mm, the appearance of sheets produced by hot press tanks is superior to those from molding presses.

5.3 Custom Carbon Fiber Parts

There are many production techniques for carbon fiber parts, each with its own advantages and disadvantages. The choice of production technique depends on the complexity of the part, strength requirements, appearance requirements, and anticipated production quantity. Here, we'll only introduce some commonly used production techniques.


5.3.1 Hand Layup and Vacuum Bagging

Hand lay-up process refers to the method of manually laying fiber-reinforced materials and resin on a mold, curing at room temperature (or with heating), and demolding to form the product under no pressure (or low pressure) conditions. It is the earliest and simplest method.

Advantages:

  • Low mold cost

  • Simple production process

  • Not limited by product size and shape

  • Suitable for producing large-sized, small-batch, and complex-shaped products

  • Versatile, can be combined with other materials such as metals, wood, and plastic foam

Disadvantages:

  • All processes cannot be quantified

  • Highly dependent on the operator's skill level

  • Difficult to control carbon fiber content

  • Issues with poor impregnation of carbon fiber/resin and incomplete curing may lead to quality problems such as cracks, fractures, and blade deformation

  • Long process cycle and poor working environment, not suitable for mass production.


5.3.2 Vacuum-Assisted Resin Transfer Molding (VARTM) 

Vacuum bag molding refers to placing pre-impregnated parts in a vacuum bag, using vacuum suction to create a negative pressure environment. This tightly adheres the carbon fiber composite material to the mold, and then curing it at room temperature or in an oven.

Advantages:

  • Short production cycle

  • Low cost

  • Suitable for producing carbon fiber parts of various shapes and sizes

Disadvantages:

  • The molding quality may not be very stable since it relies on negative pressure to adhere the material to the mold

  • Attention is needed to prevent issues like voids or bubbles.

5.3.3 Mold Pressing Method

In compression molding, curing temperature for cold pressing is between 40-50°C, while for hot pressing, it ranges from 100-170°C. The molding cycle is typically 5-60 minutes per batch, with molding pressure ranging from 10-40 MPa. Steel molds are commonly used, although fiberglass can be used for cold molds. Product dimensions are limited by mold size and press tonnage. Equipment such as hydraulic presses, heated molds, and cooling molds are required. This method is suitable for medium-batch production ranging from 100-20000T, offering high cost-effectiveness for carbon fiber parts.

Advantages:

  • High precision and repeatability in product dimensions due to mold heating and pressure treatment

  • Smooth surface finish, allowing for complex product structures to be molded in a single operation

Disadvantages:

  • Requires high requirements for the design of carbon fiber pre-impregnated layers and mold structures

  • Proper mold design can reduce structural defects and deformation issues in products

Our company has years of experience in developing and making carbon fiber parts. We have an engineering team dedicated to providing design and development services, with compression molding and vacuum bag molding as our main techniques.


6.Carbon Fiber Properties


Due to its lightweight, high strength, fatigue resistance, corrosion resistance, conductivity, magnetism, biocompatibility, and X-ray shielding properties, carbon fiber composite can be widely used in industries such as aerospace, medical, and sports equipment. The density of carbon fiber is 1.6 to 1.8 g/cm3, less than one-fourth that of steel, with a strength five times that of steel. 


However, the performance of carbon fiber products is mainly limited by the resin used. Carbon fiber can withstand temperatures up to 2000 degrees Celsius, so the temperature resistance of the resin determines the upper temperature limit of carbon fiber products.

6.1 Carbon Fiber Strength

The carbon fiber material properties are outstanding. The carbon fiber tensile strength is above 3500 MPa, which is 7-9 times that of steel, and the young’s modulus of carbon fiber ranges between 23000-43000 MPa. Therefore, the specific strength of carbon fiber, the strength-to-density ratio, can reach over 2000 MPa/(g/cm3), while for steel, it is 59 MPa/(g/cm3). And the compression strength of carbon fiber is 1-3Gpa.


6.2 Is Carbon Fiber Conductive?

Carbon fiber has excellent electrical conductivity, with a resistivity of around 10^-5 Ω·m and a conductivity of over 1000 S/m. The carbon fiber electrical conductivity mainly depends on the fiber structure and the type and amount of conductive fillers, which can be tens to hundreds of times better than most common metals. Therefore, carbon fiber is widely used in electronics, communications, conductive materials, medical imaging and treatment, battery, and supercapacitor manufacturing industries.

6.3 Carbon Fiber Thermal Conductivity

The thermal conductivity of carbon fiber generally ranges from 0.6 to 6.0 W/mK. The difference in thermal conductivity is mainly due to the properties of the composite resin, the laying method, and the fiber volume content. Carbon fiber exhibits good thermal conductivity in the direction of the filaments, which is mainly used in electronic and electrical heat dissipation materials to solve heat dissipation issues for high-density integrated electronic components, LEDs, and so on.

6.4 Carbon Fiber Thermal Expansion

The thermal expansion coefficient refers to the change in dimensions such as length, width, thickness, or aperture of a solid when heated. At an ambient temperature of 20-70°C, the thermal expansion coefficient of T300 carbon fiber is -0.74×10^6/K, and for M40 carbon fiber, it's -1.23×10^6/K. Larger product dimensions result in greater deformation due to thermal release during molding.

6.5 Corrosion Resistant and Chemically Stable

Carbon fiber forms a stable graphite crystal structure at high temperatures, providing excellent corrosion resistance. Additionally, the resin matrix in carbon fiber composites is inert, offering additional chemical stability. Therefore, carbon fiber composites can be used in various harsh environments, such as in seawater or environments with chemical substances.


7. Carbon Fiber Application

Carbon fiber is used as acarbon fiber reinforced plastic material known for its lightweight, high strength, corrosion resistance, and low coefficient of thermal expansion. With increasing production capacity and decreasing production costs, its applications are becoming more widespread.

7.1 Aerospace Industry:

Carbon fiber was first used in the aerospace industry. Compared to metal materials, it significantly reduces component weight, enhances payload and fuel efficiency, and improves the mechanical performance and durability of aerospace vehicles.

7.2 Automotive Industry:

In the automotive sector, carbon fiber is used in components such as body panels, frames, seats, and interior/exterior trims. It enhances vehicle performance and comfort, reduces vehicle weight, improves fuel efficiency, and promotes energy savings and environmental protection.

7.3 Energy Sector:

In the energy sector, carbon fiber is primarily used in wind turbine blades. Leveraging its advantages of being lightweight and fatigue-resistant, it improves wind power generation efficiency and stability while reducing maintenance costs.


8.What Is Carbon Fiber Quality?

You can get carbon fiber composite parts, by combining carbon fiber and resin. The quality of carbon fiber parts depends on the carbon fiber materials, structural design, and surface treatment.

8.1 Materials selection

Performance: The selection of carbon fiber yarn and resin is crucial for mechanical properties.

Appearance: To ensure a perfect finish, it's important to choose prepreg materials with consistent color and no discoloration and the neat texture.

8.2 Strength

In the product design phase, proper carbon fiber tow strength, lamination design, and structural design are chosen to meet strength requirements. However, molds and prototypes need to be produced and tested with equipment and actual assembly to verify if the samples meet usage requirements.

8.3 Appearance

Qualified carbon fiber parts should have a smooth, flat surface without bumps, dents, scratches, or cracks.

Exterior parts typically need a matte or glossy paint finish, requiring skilled manual sanding and painting. Any paint color discrepancies are unacceptable; if repairs are needed, the entire part must be sanded and repainted to avoid color difference.

Due to the expansion characteristics of carbon fiber, CNC machining is required for post-processing. The finished product should have no cracks, cuts, burrs or deformations.

Conclusion:

With the advancement of carbon fiber technology and increased production capacity, carbon fiber is becoming more and more popular. More industrial components and everyday products will incorporate carbon fiber composites. Our company has years of experience in research, development, and production. If you have any needs for custom carbon fiber products, feel free to leave us a message or send an inquiry. We're more than happy to offer our proposal and suggestions.



Carbon fiber 101:

  1. What Is Carbon Fiber Made Of?

-Carbon fiber is made from organic polymer compounds, and over 90% of the output is made from polyacrylonitrile (PAN).

  1. What Is Carbon Fiber Cloth?

-Also known as carbon fiber fabric, it's made by machines weaving carbon fiber tow  into various patterns, making it more elegant and convenient to work with. It enhances structural strength according to application and is commonly made in plain, twill, specific patterned satin weaves, and unidirectional fabric.

  1. What Is Carbon Fiber Wrap?

-Carbon fiber wrap and vinyl is a type of carbon fiber sticker that mimics the pattern of carbon fiber. They look similar to carbon fiber patterns but lack the three-dimensional feel. In terms of performance and structure, they are far from real carbon fiber. Their price is just that of regular stickers, much lower than real ones.


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